@Divinitize - I have some code you may find interesting, for making a UTexture2D out of a color data buffer.
If you want it I can clean it up and send it over, it should be possible to create a more robust whiteboard using it by simply keeping around a buffer of your color data and updating the texture each time the user changes the data in the buffer. Then it’s just a matter of setting the texture onto a dynamic material instance (to be used by the whiteboard mesh).